Japanese Patent Unexamined Publication No. 61-213556 (entitled "STARTING METHOD FOR COMPRESSION TYPE REFRIGERATOR") is referenced as a conventional example relating to a starting method for a compressor. In a refrigerator provided with a compressor such as a scroll-type compressor in which a direction of flow of gas is reversed by reversing a rotational direction of a drive shaft, it is difficult to rotate the drive shaft in a normal forward direction because of a large amount of coolant liquid which collects and becomes stagnant in the compressor when the refrigerator is off. However, the publication discloses a technique wherein the compressor is first rotated in the direction opposite to the normal direction at the start-up to discharge the liquid in the compressor mechanism, thereby avoiding both the starting difficulty of the compressor and damage to the compressor. This published patent points out two common phenomena to be avoided by the embodiments thereof. First, the compressor when rotated in the reverse direction generates noise when the normal operation is stopped. Second, a check valve or the like, which is generally provided on the suction side for coping with a problem such as stagnation of a part of the oil in the suction passage, would hinder the first reverse rotation of this starting method. The publication discloses a method for dispensing with the check valve, which would otherwise hinder the reverse rotation in the starting period, by switching a four-way valve into a reverse mode when the refrigerator is stopped from the normal operating condition.
In the above-described conventional starting method of the refrigerator, it is necessary to provide the four-way valve and a mechanism for switching over the four-way valve when the compressor is stopped. Upon switching over the four-way valve, a large reverse flow noise and collision would be generated. Depending upon the operating condition of the refrigerator, there is a risk that the compressor would start the reverse rotation to generate noise until the pressures are stabilized at respective parts of the refrigerator after the four-way valve of the compressor has been switched. In addition, in the case of a refrigerator without any four-way valve, it is necessary to provide an electromagnetic valve instead of the four-way valve, which increases the total cost of the refrigerator.